Added a second router, cannot connect to WDMCH with wifi of second router

Hello, I have recently added a second router to my home network. The setup is GPONModem>>Router1>>Router2. WDMCH is connected via ethernet cable coming from Router1. When my MacBook is connected to WiFi on Router2 I can access the files (movies, pictures etc) on WDMCH, however, Time Machine stops seeing the WD for back-ups. If I switch my MacBook to WiFi of Router1 Time Machine gets connected and starts back-up (other files still visible). Would this be a set-up issue with WDMCH or Time Machine?
Many thanks in advance